In one aspect, the present invention relates to certain monolayer, biaxially oriented blown nylon film materials and to a process for the preparation thereof. In another aspect, such invention relates to a process for the preparation of such films on conventional polyethylene blown film equipment. In a further aspect, this invention also relates to an improved process for the preparation of blown monolayer nylon films on specially designed extrusion equipment which is conventionally used in the preparation of monolayer blown nylon films.
Polyamide resins, commonly referred to as nylon, and blends thereof with various other polymeric materials such as polyethylene, graft or random copolymers of ethylene with ethylenically unsaturated carboxylic acids or anhydrides, ethylene/vinyl acetate copolymers, ethylene/alkyl acrylate copolymers and the like are well known in the art and have been proposed for use in the fabrication of a variety of thermoplastic articles such as, for example, various molded parts, and extruded articles including fibers, filaments, tubing, bottles, films, sheets, wire coatings and the like. See, for example, British Pat. No. 998,439; British Pat. No. 1,262,802; British Pat. No. 1,464,036; British Pat. No. 1,552,352; U.S. Pat. Nos. 3,093,255; 3,250,823; 3,373,223; 3,373,224; 3,472,916; 3,668,274; 3,676,400; 3,681,216; 3,822,227; 3,845,163; 3,963,799; 3,997,625; 4,018,733; 4,035,438; 4,086,295; 4,100,238; 4,105,709; 4,160,790; 4,174,358; 4,251,424; 4,261,473; 4,287,315; 4,305,865; and 4,321,336; Japanese Pat. No. J7 4049-179; EPO Application No. 27191; and published Japanese Patent Applications Nos. J5 0142-675; J5 4155-270; J5 4155-272; J5 4016-576; J5 5034-956; J5 6004-652 and J5 6062-864.
Historically, certain features or characteristics of polyamide resins have tended to hinder the manufacture of polymer film structures therewith. For example, such resins typically have relatively low melt tension properties and relatively low melt viscosity at the temperatures involved in extrusion processing and particularly at high rates of shear. Such characteristics have been especially troublesome relative to the manufacture of blown polyamide film structures, particularly in the case of monolayer blown polyamide film structures. In particular, an extruded, molten web or mass of such polymer generally fails to have sufficient strength to suitably support a hot film bubble as is necessary in conventional blown film manufacturing operations. Accordingly, it has been common practice in the past to resort to special processing techniques (e.g., cast film preparation followed by special tentering/stretching operations), special equipment design (e.g., special die designs), special extra high molecular weight polyamide compositions, special multiple layered film structures and the like when the objective was to prepare a biaxially oriented polyamide film structure.
In view of the foregoing, it would be highly desirable to provide a means for improving the processability of polyamide resin compositions and to thereby facilitate and simplify the fabrication of biaxially oriented, blown film structures therefrom. Moreover, it would also be highly desirable to provide a means or process by which biaxially oriented monolayer polyamide film structures could be suitably prepared using conventional polyolefin blown film manufacturing equipment.